1. Field of the Invention
The present invention relates to an optical pickup device which can execute a process of recording in a high quality on a media such as a CD-R (Compact Disc-Recordable).
2. Description of the Related Art
FIG. 5 is an explanatory diagram showing one form of an optical pickup device in a related art. FIG. 6 is an explanatory diagram showing a state in which an interference of light has occurred due to an internal reflection of light within a reflect mirror within the exemplified structure.
An optical pickup device 501 (FIG. 5) is used to record or replay data such as information to or from a media 900. Examples of the media 900 include, for example, read-only optical disks such as a CD-ROM and a DVD-ROM and write-once optical disks such as a CD-R and DVD±R.
The term “CD” is an abbreviation for a “Compact Disc”, “DVD” is an abbreviation for “Digital Versatile Disc” or “Digital Video Disc”, and “ROM” as used in “CD-ROM” and “DVD-ROM” is an abbreviation for “Read Only Memory”. With a CD-ROM or DVD-ROM, data can only be read, but data can be written to the CD-R or DVD±R, where the “R” stands for “Recordable”.
The optical pickup device 501 replays data recorded on various optical disks or records data on various recordable or rewritable optical disks. The optical pickup device 501 corresponds to a CD-based media and a DVD-based media.
An electrical current is supplied from a laser driver 510 for CD to a light emitting element 520 for CD and laser light is output from the light emitting element 520 for CD. As the light emitting element 520 for CD, a laser diode (LD) is used. The LD 520 for CD is stored within a laser holder 530. The laser holder (LD holder) stores the LD.
Information is recorded on a disk 900 such as the CD-R or information recorded on the disk 900 such as the CD-R is replayed using the laser light which is emitted from the LD 520 when an electrical current is supplied from a laser driver (LDD) 510 to the LD 520.
The laser light emitted from the LD 520 transmits through a ½ wave retardation plate (HWP)-plus-diffraction grating 540 and a divergent lens 550, is reflected at an approximate right angle in and transmits through a first beam splitter 560, transmits through a second beam splitter 660, is reflected by a reflect mirror (RM) 800 at an approximate right angle, transmits through a collimator lens (CL) 710, a ¼ wave retardation plate (QWP) 720, and an objective lens (OBL) 730, and is irradiated onto the disk 900.
In the HWP-plus-diffraction grating 540, an HWP and a diffraction grating are combined as one structure. The diffraction grating splits laser light emitted from the LD into a plurality of components using diffraction of light. More specifically, the diffraction grating functions to separate the laser light emitted from the LD into one main beam and two sub-beams taking advantage of diffraction of light. The HWP has a function to change, with regard to the polarization characteristic of the laser light, a direction of polarization of linear polarization of laser light. The HWP is also called a ½λ (lambda) plate. The HWP-plus-diffraction grating has the characteristics of the HWP and the diffraction grating.
The divergent lens 550 focuses laser light emitted from the LD 520.
The beam splitter (BS) 560 shown in FIG. 5 reflects, with regard to the polarization direction of the laser light, an S wave and allows a P wave to transmit. A term “P” in “P wave” is an abbreviation of “parallel” in German and means “parallel”. A term “S” in “S wave” is an abbreviation of the German word “senkrecht” meaning “vertical”. The BSs 560 and 660 have different characteristics depending on the wavelength for CD and the wavelength for DVD.
Most of the laser light is reflected by the RM 800, but a portion of the laser light is transmitted. In the RM 800, a surface 801 from which the laser light enters is made into a coated smooth surface. In addition, a surface 802 in the RM 800 from which the laser light exits is also made into a coated smooth surface.
A CL 710 indicated by a solid line converts light entering the lens 710 from the side of the RM 800 into specular light and emits the specular light to the side of the OBL 730. Specular light is light in which the light beam does not widen but is transmitted in parallel. Diffuse light, on the other hand, refers to light from a light source which irradiates light in a manner such that the light diffuses in various directions.
The QWP 720 converts linearly polarized light into circularly polarized light or circularly polarized light into linearly polarized light.
The OBL 730 has a function to focus laser light emitted from the LD 520 or LD 620 on the disk 900. The OBL 730 is equipped on a lens holder (not shown).
A portion of the laser light output from the LD 520 transmits through the HWP-plus-diffraction grating 540 and the divergent lens 550, is reflected at an approximate right angle in and transmits through the first BS 560, transmits through the second BS 660 and the RM 800, and is incident on a photodetector 740. The photodetector 740 is formed as a front monitor diode (FMD) 740 onto which a portion of the laser light is irradiated. The FMD is a photodetector which monitors the laser light output from the LD and applies a feedback for control of the LD.
A portion of the laser light reflected by the disk 900 transmits through the OBL 730, QWP 720, and CL 710, is reflected at an approximate right angle in the RM 800, transmits through the second BS 660, the first BS 560, and an anamorphic lens 750, and is incident on a photo diode IC (PDIC) 760.
The anamorphic lens 750 creates an astigmatism of laser light. The astigmatism means a defocus.
The PDIC 760 is a photodetector which receives laser light reflected by the disk 900, converts the received laser light into an electrical signal, and detects information recorded on the disk 900. The PDIC 760 is also a photodetector which receives laser light reflected by the disk 900, converts the received light into an electrical signal, and operates a servo mechanism (not shown) of a lens holder (not shown) with OBL 730 which is a part of the optical pickup device 501. A servo mechanism is a mechanism which measures a state of a target of control, compares the measured state with a reference value, and automatically applies a correction control.
An electrical current is supplied from a laser driver 610 for DVD to a light emitting element 620 for DVD and laser light is output from the light emitting element 620 for DVD. The LD 620 for DVD is stored in a laser holder 630. Information is recorded on the disk 900 such as a DVD-R or information recorded on the disk 900 such as a DVD-R is replayed using the laser light emitted from the LD 620 when the electrical current is supplied from the LDD 610 to the LD 620.
The laser light output from the LD 620 transmits through a divergent lens 640 and a HWP-plus-diffraction grating 650, is reflected at an approximate right angle in and transmits through the BS 660, is reflected by the RM 800 at an approximate right angle, transmits through the CL 710, QWP 720, and OBL 730, and is irradiated onto the disk 900. The HWP-plus-diffraction grating 650 is a structure in which an HWP and a diffraction grating are combined.
A portion of the laser light output from the LD 620 transmits through a divergent lens 640 and the HWP-plus-diffraction grating 650, is reflected at an approximate right angle in and transmits through the BS 660, transmits through the RM 800, and is incident on the photodetector 740.
A portion of the laser light reflected by the disk 900 transmits through the OBL 730, QWP 720, and CL 710, is reflected at an approximate right angle in the RM 800, transmits through the second BS 660, first BS 560, and anamorphic lens 750, and is incident on the PDIC 760.
The LDD 510, LD 520, LDD 610, LD 620, FMD 740, and PDIC 760 are connected to a flexible substrate 505 such as a flexible printed circuit (FPC) in an electrically conductive manner. In the FPC 505, a plurality of circuit conductors 505p are printed on an insulating sheet 505q, metal foils 505p such as, for example, copper foils are provided on the insulating sheet 505q in parallel, and a protection layer which is transparent or semitransparent (not shown) is provided on the metal foils.
In addition, there also exist a low-cost optical pickup device and an optical pickup device for a phase-change optical disk in which a semiconductor laser of a lower power can be used by forming a hologram in a shape of stairs to improve the diffraction efficiency of the light by each hologram.
In recent years, there has been a demand for further reduction in thickness and size of the optical pickup device 501 (FIG. 5). In order to reduce the thickness of the optical pickup device 501, a configuration has been considered in which the CL 710 and the QWP 720 shown by a solid line and positioned between the RM 800 and the OBL 730 are moved to a position between the second BS 660 and the RM 800 as a CL 710X and QWP 720X shown by a virtual line.
However, in the optical pickup device 501 having such a configuration, as shown in FIG. 6, an internal reflection of light occurs in an inside 804 of the RM 800 and, as a result, an interference of light occurs. The laser light transmitting from the second BS 660 (FIG. 5) through the CL 710X to the QWP 720X becomes specular light. When the laser light becomes specular light, an internal reflection occurs in the inside 804 of the RM 800 (FIG. 6) and interference of light results.
Here, interference of light refers to a phenomenon in which waves of light are superposed to result in intensified or weakened light. The interference of light does not occur in the optical pickup device 501 (FIG. 5) when the laser light is diffuse light and only occurs when the laser light is specular light.
When interference of light occurs due to internal reflection of light in the inside 804 of the RM 800 (FIGS. 5 and 6), the laser light irradiated onto the FMD 740 (FIG. 5) becomes unstable. In such a situation, the electrical current output from the FMD 740 fluctuates.
Because the FMD 740 monitors a portion of light transmitting through the RM 800, when interference of light occurs due to occurrence of the internal reflection of light in the RM 800 (FIG. 6), the amount of light transmitting through the RM 800 changes.
Consequently, the amount of light incident on the FMD 740 (FIG. 5) fluctuates, such that the amount of current supplied from the FMD 740 also fluctuates. When the amount of current supplied from the FMD 740 fluctuates, the power of the laser light emitted from the LD 520 or LD 620 also fluctuates.
Because the FMD 740 monitors the laser light output from the LD 520 or LD 620 and applies feedback for controlling the LD 520 or LD 620, when the amount of current supplied from the FMD 740 fluctuates, the power of the laser light emitted from the LD 520 or LD 620 also fluctuates.
There is a concern that, as a result of the above-described phenomenon, problems may result when data is written to the disk 900 such as CD-R or data is replayed from the disk 900 such as CD-R.
For example, when the intensity of laser light emitted from the LD 520 or LD 620 becomes unstable while data is being written to the optical disk 900 and a recording deficiency occurs on the optical disk 900, there may be cases that the recorded content on the optical disk 900 cannot be read using various optical disk devices (not shown). When the reading of media such as the optical disk 900 cannot be performed because of a recording deficiency on the media such as the optical disk 900, the optical disk 900 is wasted.